The purchase of a cell sorter for interdepartmental use at the Pennsylvania State University is proposed. The major piece of equipment to be acquired is a Coulter Electronics, Inc. Electronically Programmable Individual Cell Sorter "EPICS V". This is to be used in four major NIH-sponosred research projects: quantitation and characterization of herpes simplex virus type 2 antigens in transformed cells and human neoplasms; a study of the source and regulation of hematopoietic stem cells during early embryogenesis; the purification and characterization of the hormone-responding prolactin-secreting cells of the mammalian anterior pituitary; testing the specificity of merocyanin dyes in hematopoietic and leukemia cell identification, and monitoring red-cell mediated microinjection of macromolecules into leukemic and other cells. Access to use of the facility will be made available to other users on the advice of an internal advisory committee. Such projects presently include the purification of human kidney plasminogen-activator producing cells, the purification of rat and human growth-hormone producing cells, cell-cycle progression of radiation-damaged cultured cells, insect virus host specificity, sorting of potato mesophyll protoplast fragments for fusion with whole protoplasts, classification of lymph-node cells that respond to tumor promoting agents, characterization of the hormone dependence of cell-cell interactions in a rat mammary ascites tumor, differential characterization of pre-stalk and pre-spore cells in the differentiating cellular slime mold Dictyotelium discoideum.